// Source : https://leetcode.com/problems/number-of-students-unable-to-eat-lunch/
// Author : Hao Chen
// Date   : 2021-05-10

/***************************************************************************************************** 
 *
 * The school cafeteria offers circular and square sandwiches at lunch break, referred to by numbers 0 
 * and 1 respectively. All students stand in a queue. Each student either prefers square or circular 
 * sandwiches.
 * 
 * The number of sandwiches in the cafeteria is equal to the number of students. The sandwiches are 
 * placed in a stack. At each step:
 * 
 * 	If the student at the front of the queue prefers the sandwich on the top of the stack, they 
 * will take it and leave the queue.
 * 	Otherwise, they will leave it and go to the queue's end.
 * 
 * This continues until none of the queue students want to take the top sandwich and are thus unable 
 * to eat.
 * 
 * You are given two integer arrays students and sandwiches where sandwiches[i] is the type of the 
 * ith sandwich in the stack (i = 0 is the top of the stack) and students[j] is the preference of 
 * the jth student in the initial queue (j = 0 is the front of the queue). Return the number of 
 * students that are unable to eat.
 * 
 * Example 1:
 * 
 * Input: students = [1,1,0,0], sandwiches = [0,1,0,1]
 * Output: 0 
 * Explanation:
 * - Front student leaves the top sandwich and returns to the end of the line making students = 
 * [1,0,0,1].
 * - Front student leaves the top sandwich and returns to the end of the line making students = 
 * [0,0,1,1].
 * - Front student takes the top sandwich and leaves the line making students = [0,1,1] and sandwiches 
 * = [1,0,1].
 * - Front student leaves the top sandwich and returns to the end of the line making students = 
 * [1,1,0].
 * - Front student takes the top sandwich and leaves the line making students = [1,0] and sandwiches = 
 * [0,1].
 * - Front student leaves the top sandwich and returns to the end of the line making students = [0,1].
 * - Front student takes the top sandwich and leaves the line making students = [1] and sandwiches = 
 * [1].
 * - Front student takes the top sandwich and leaves the line making students = [] and sandwiches = [].
 * Hence all students are able to eat.
 * 
 * Example 2:
 * 
 * Input: students = [1,1,1,0,0,1], sandwiches = [1,0,0,0,1,1]
 * Output: 3
 * 
 * Constraints:
 * 
 * 	1 <= students.length, sandwiches.length <= 100
 * 	students.length == sandwiches.length
 * 	sandwiches[i] is 0 or 1.
 * 	students[i] is 0 or 1.
 ******************************************************************************************************/

class Solution {
public:
    int countStudents(vector<int>& students, vector<int>& sandwiches) {
        int st[2] = {0};
        for(auto s: students) {
            st[s]++;
        }
        int cnt = 0;
        for(auto& san : sandwiches){
            if (st[san] == 0) break;
            st[san]--;
            cnt++;
        }
        return students.size() - cnt;
    }
};
